Retrieving hydrocarbons from subterranean reservoirs is becoming more difficult, as existing reserves are depleted and production becomes more expensive. It has been estimated that mature fields account for up to 70% of the world's production or more. In order to increase production, reservoirs are often hydraulically fractured to stimulate production of hydrocarbons from the wellbore. Hydraulic fractures are created in subterranean formations by hydraulically injecting water or high viscosity fluid (also referred to as fracturing fluid) containing a proppant at a high flow rate into a wellbore and forcing the fracturing fluid against the formation strata by pressure. The formation strata or rock is forced to crack, creating or enlarging one or more fractures. The proppant subsequently prevents the fracture from closing completely and thus provides improved flow of recoverable fluid, i.e., oil, gas or water.
Because aging wells are often produced from multiple intervals, some very thin, the ability to locate these stimulation treatments with pinpoint accuracy is a key to more effective remediation and increased ultimate recovery. Also in more “non-conventional” plays like the fractured shales, the quality and extent of the fracture job is paramount to the financial success of the well and the play. However, few methods exist for accurately visualizing fracture length, proppant penetration, and estimated flow in the new fracture to accurately assess production capabilities and the need for further remediation before production is initiated.
Some technologies have tried to determine the extent and position of a fracturing using various imaging techniques. For example, Hocking et al., U.S. Pat. No. 6,330,914 provides a method for monitoring a propagating vertical fracture in a formation by injecting conductive fracture fluid into the formation to initiate and propagate the fracture; energizing the fracture fluid via an electrical voltage while the fracture propagates; and measuring the inducted electromagnetic field parameters to judge about the fracture development and geometry. Further, McCarthy, et al., WO2007013883, provides introducing a target proppant; transmitting electromagnetic radiation from about 300 megahertz-100 gigahertz; and analyzing a reflected signal from the target particle to determine fracture geometry. Lastly, Nguyen et al., U.S. Pat. No. 7,073,581, describes electro-conductive proppant compositions and related methods of obtaining data from a portion of a subterranean formation.
Each of these techniques, however, seem to rely on detecting data utilizing a series of sensors connected to recording equipment, that multiplexes the data and records the measured voltage via a wire based system or collects data by sensors located at the well bore or adjacent well bores. Having numerous sensors and bulky wiring systems laying on the ground around an active drill rig and production site is a recipe for system failures, lost data due to failures in timing and communication, and broken or crushed wires. These and other techniques for detecting fracture geometry fail to account for how to actually measure the data in the field, which is a critical step in the practical success of evaluating and measuring the geometry of a fracture.
Knowing, measuring and translating data from various sensors and tools is of primary importance to the geophysicists and the drilling and completion engineer in order to determine if fracturing was successful and as a predictor of expected production rates from the well. Furthermore, the ability to determine the fracture geometry in 3D and 4D provides enhanced recovery data. It is therefore an object of the present invention provide a method and apparatus for evaluating and measuring the geometry of a fracture.